Machine for forming metal bars

ABSTRACT

A machine for forming metal bars, in particular for producing ingots made of precious metal such as gold, silver, precious alloys, as well as other pure metals or different alloys, including a melting station for melting the metal contained in an ingot mould, wherein the ingot mould contains an accurate amount of metal, in the form of powder, grits or swarf of various sizes and a chemical additive, which creates a chemical reaction with the impurities contained in the metal. The chemical additive may be any of boric acid, borax, potassium nitrates, ammonium, sodium, lithium and potassium and sodium chlorides.

This is a divisional application of U.S. patent application Ser. No.14/007,910, filed Oct. 17, 2013, which in turn is the National Stage ofPCT/EP2012/001377 filed on Mar. 29, 2012, which claims priority under 35U.S.C. §119 of Italian Application No. VI2011A000076 filed on Apr. 1,2011. The international application under PCT article 21(2) waspublished in English. The disclosure of the referenced applications areincorporated herein by reference.

The present invention regards a machine for forming metal bars, inparticular for producing ingots made of precious metal such as gold,silver, precious alloys, as well as other pure metals or differentalloys.

As known, producing ingots, in particular made of gold, silver, preciousalloys, other pure metals and different alloys, is usually obtained bymeans of two different methods.

When producing light ingots, from 5 g up to 50 g, there is used a coldmoulding and coining process, starting from semi-finished products, suchas cylindrical-shaped preformed pads or billets.

When producing ingots with weight varying between 50 g and 50 Kg thereis instead used the melting method and subsequent solidification of themetal in the special moulds. In practice, the metal to be melted isplaced within ladles, in form of powders, granules or loose rawmaterials of various sizes, wherein it is brought to melting. Then themolten metal is poured in single ingot moulds, generally shaped to forma truncated-trapezoid wherein, solidifying, it takes the form of aningot.

Such two operations, the melting one and the subsequent one forsolidifying the material, must be carried out with special care, giventhat the obtained end-product must meet strict and specific standardrequirements.

Actually the ingots available in the market, besides having an exactpurity if made of pure metal, or an exact percentage of pure metal ifmade of an alloy (the so-called “count”), must have extremely precisedimensions and weight, an external configuration with regular surfaces,without depressions or cracks, a uniform coloration and, above all, theymust have a perfect internal metal-graphic structure, without blowholes,microporosities and structural tensions.

In order to avoid obtaining faulty ingots not capable of allowingobtaining “punching”, which would thus be considered as waste material,it is necessary that the entire production cycle be carried out withmuch care, in particular during the steps of melting, solidifying andcooling the metal.

An object of the present invention is to provide a machine for formingmetal bars, in particular for producing ingots, made of precious andnon-precious material and, which does not have the drawbacks revealed bythe plants of the known type.

The characteristics of the invention will be made more clear through thedescription of a possible embodiment thereof, provided by way ofnon-limiting example, with reference to the attached drawings, wherein:

FIG. 1 represents an elevational view of the machine according to theinvention.

As observable from the drawing, the machine according to the invention,generally indicated with reference 100, comprises a melting station,indicated with reference 102, for melting the metal contained in theingot moulds, indicated with reference 1.

As can be seen in FIG. 1, on a loading surface of the first operatingstation 101 there are positioned the empty ingot moulds 1, interposingbetween an ingot mould and the subsequent one or between groups of twoor more mutually adjacent ingot moulds, spacers 2, made of graphite orany other refractory material. Spacers 2 serve the function ofmaintaining a predefined distance between the single ingot moulds orbetween the groups of ingot moulds, in a manner such that the ingotmoulds 1, forming a “train of ingot moulds” are positioned, during theforward movement, always correctly within the work area. Furthermore,said operating surface is also provided with a pushing device 3, drivenvariously, such as by a worm screw, a pneumatic means, hydraulic meansor any other means, which provides for pushing, with a predefined“pitch”, the aforementioned train forward, and then returning and thusfreeing space on the aforementioned loading surface, to allow depositingfurther empty ingot moulds.

According to the invention, in each single ingot mould 1 there is pouredan exact weight of metal, in form of powder, grits or swarf of varioussizes and there is added a chemical additive, which creates a chemicalreaction with the impurities contained in the metal and which is made upof boric acid, borax, potassium nitrates, ammonium, sodium, lithium andpotassium and sodium chlorides, used separately or mixed. Lastly, insaid first station 101 there occurs the positioning of the cover 4 forclosing the filled ingot mould.

Then, the pushing device 3 pushes the “train” from the station 101 forsupplying the ingot moulds to the melting station 102, wherein there maybe a heating furnace 5, in which the ingot moulds and the spacers slideon a refractory surface in absence of controlled atmosphere, or a tunnel6, in which the ingot moulds and the spacers slide on the surface of thetunnel or on guides, variously heated, through electrical resistors, byelectromagnetic induction, through burners of the gas type or of anyother type, up to the operating temperature. By way of example,regarding the ingots made of silver (Ag) such temperature is of about1150° C. While for the ingots made of gold (Au) it is of about 1250° C.and in the tunnel or in the guides there is insufflated inert gas, suchas nitrogen, nitrogen-hydrogen mixture with maximum 4.5% of hydrogen(H), to create an “inert” environment, which prevents the ingot mouldsand the covers from being subjected to oxidation and thus prevents quickwearing and keeps the molten metal protected from oxygen.

Furthermore, with the aim of reducing the heat and the atmosphere of theinert gas, within the tunnel 6 there is provided for, at the lateralopenings for the inlet and outlet of the “train”, the application ofmobile partitions 7 obtained, for example, with the guillotinetechnique, which create a mobile or flexible insulating refractorybarrier, the movement thereof being manual or automatic.

Then, still from an operational point of view, once the melting timeelapses there is activated the pushing device 3, which provides formoving the “train” forward. The ingot moulds present on the loadingsurface are pushed into the furnace/tunnel 5/6 and the same, in turn,push the ingot moulds present in the tunnel/furnace 5/6 to exit, withthe aim of allowing the latter, containing the molten metal, then topass in the station of “secondary addition” 103 and, subsequently, inthe solidification station 104.

From an operational point of view, in the station 103 there occurs theraising of the cover of the ingot mould, by means of grippers of themechanical type, pneumatic type or any other type, while dosing systemsof the mechanical type, pneumatic type or any other type, add in eachsingle ingot mould 1, on the molten metal, an accurate amount ofchemical additive (dosing element “C”), which creates a chemicalreaction with the impurities contained in the molten metal. The additivebeing made up of boric acid, borax, potassium nitrates, ammonium,sodium, lithium and potassium and sodium chlorides, used separately ormixed. Subsequently, the cover is repositioned on the ingot mould.

Also in the process of “secondary addition” there should be created an“inert” environment, regarding which there is introduced a flow of inertgas such as nitrogen, argon or nitrogen-hydrogen mixture, which preventsoxidation of the ingot moulds and the covers and protects the metalstill in liquid form against oxygen.

Due to construction reasons, in some cases the “secondary addition”station 103 and the solidification station 104 may be incorporated in asingle station 103/104, where the addition and solidification steps areperformed sequentially.

The invention thus conceived can be subjected to numerous variants andmodifications and the construction details thereof can be replaced bytechnically equivalent elements, all falling within the inventiveconcept defined by the following claims.

1. A machine for forming metal bars, in particular for producing ingotsmade of precious metal such as gold, silver, precious alloys, as well asother pure metals or different alloys, comprising a melting station formelting the metal contained in at least one ingot mould which includes acover, wherein said at least one ingot mould comprises an accurateamount of metal, in the form of powder, grits or swarf of various sizesand a chemical additive, which creates a chemical reaction withimpurities contained in the metal wherein said chemical additive isselected from the group consisting of boric acid, borax, potassiumnitrates, ammonium, sodium, lithium and potassium and sodium chlorides,and combinations thereof.
 2. The machine according to claim 1, whereinsaid melting station comprises at least one melting furnace in which oneor more ingot moulds containing said metal and said chemical additiveare pushed.
 3. The machine according to claim 1, comprising a station ofsecondary addition said station of secondary addition adding an accurateamount of a second chemical additive in each ingot mould, on the moltenmetal, said accurate amount of said second chemical additive creating achemical reaction with the impurities contained in said molten metal,said second chemical additive being selected from the group consistingof boric acid, borax, potassium nitrates, ammonium, sodium, lithium andpotassium and sodium chlorides, and combinations thereof.
 4. The machineaccording to claim 3, wherein said station of secondary additioncomprises dosing systems that add said second chemical additive on thestill liquid metal contained in each ingot mold.
 5. The machineaccording to claim 3, wherein said station of secondary additioncomprises grippers that raise the cover of each ingot mould.
 6. Themachine according to claim 3, wherein said station of secondary additionis incorporated in a single station which also comprises asolidification station.
 7. The machine according to claim 3, whereinsaid station of secondary addition comprises an inert environment whichcomprises inert gas which prevents the oxidation of said ingot mouldsand said covers and protects the metal still in liquid form againstoxygen.
 8. The machine according to claim 7, wherein said inert gas isnitrogen, argon, or nitrogen-hydrogen mixture.